As the integration of a semiconductor device becomes higher, the size of the semiconductor device is reduced, and as a result, a lithography process that is used to manufacture the semiconductor device becomes more complicated. At present, as an exposure wavelength when a pattern of dense lines or a single line is formed, a wavelength of 248 nm or 193 nm is mainly used. Recently, patterning that uses a wavelength of 157 nm is gradually being used.
When the shorter wavelength is used, if the structure of a thin film, such as a photoresist, which is formed on a semiconductor substrate, is slightly changed, the resolution and depth of focus (DOF) are decreased. Accordingly, the pattern may be distorted and Line Edge Roughness (LER) may occur.
In a general lithography process, the structure of the photoresist is primarily changed during a bake process.
FIG. 1 is a cross-sectional view showing a bake oven according to the related art.
Referring to FIG. 1, the bake oven includes a heating plate 10. Heat rays 20 are provided at an upper portion inside the heating plate 10 to heat a wafer 30, and an exhaust pipe 70, through which a gas 60 is ejected, is provided at an edge of the heating plate 10.
A cover 40 is provided above the plate 10, and gas ejection nozzles 50 are provided inside the cover 40.
If the wafer 30 is heated using the heat rays 20, it does not heat uniformly over the entire surface. Accordingly, during the bake process, the gas 60 is ejected on the surface of the wafer 30 to disperse the heat.
When the thin film is formed in such a manner, during the bake process, the molecular weight of the thin film is increased by geometric progression, and the thickness of the thin film is unnecessarily increased. Accordingly, the depth of focus (DOF) is changed during an exposure process. As a result, costs for the lithography process are increased, and the efficiency of the semiconductor manufacturing process is reduced.